Defueling operations with respect to aircraft are primarily associated with servicing and maintenance of the aircraft's fuel cells. Because of the highly flammable nature of aircraft fuel, safety precautions require total removal of fuel before such cells can be worked upon. Draining of fuel from within the fuel cells consumes substantial time prior to initiation of related servicing and maintenance procedures.
In many applications, the valve stem is simply manually depressed and locked in a depressed condition to permit fuel to drain by gravity and simply fall onto the ground or other surfaces beneath the fuel drain. This results in undesirable exposure to the draining fuel by both servicing personnel and the surrounding ground surface areas.
While gravity fuel drains are provided at the lower exterior surfaces about such fuel cells, conventional manual draining procedures typically require time periods of up to 8 to 10 hours before all fuel is completely drained from within all the fuel cells of a large aircraft.
Vacuum systems have been applied to substantially reduce the time required for draining a fuel cell. By attaching a vacuum hose to a fuel drain, a vacuum system can completely drain the fuel cells of a large aircraft in a period of approximately one hour. This not only reduces delays in servicing the fuel cells, but substantially increases the available flying time for the aircraft being serviced.
Funnels have been telescopically mounted to abut the surrounding surface to release fuel from within the fuel cell by gravity through opened fuel drains. However, the use of such a funnel still requires that the fuel drain valve stem be manually depressed, which results in initial loss of fuel and presents a potentially messy manual procedure to those working under the fuel cell.
Recent systems have been developed for using vacuum pressure to speed up the draining procedure. Current vacuum systems utilize specialized fuel cell attachments designed to mechanically engage specific fuel drain configurations. This limits the use of such attachments to the specified fuel drains. Such special attachment designs require servicing personnel to maintain an inventory of attachments matching the design requirements of fuel drain cells that might be encountered at a particular facility. Because there are wide variations in fuel drain designs, depending upon specific requirements of different aircraft manufacturers and users, mechanical fuel cell attachments have been found to have very limited practical application in the field of aircraft maintenance.
The present defueling fitting is designed to provide a more universal fuel cell attachment. It can be effectively utilized in conjunction with a variety of conventional flush-mounted fuel drains used today in aircraft fuel cells. It requires no direct mechanical attachment to the fuel drain itself. It is held to the surrounding exterior aircraft surface by vacuum pressure and can be readily released after the draining procedure has been accomplished. It confines the draining fuel so that it can be directed through an attached hose to a receiving portable or stationary tank. Fuel can be drained through the fitting by gravity or by a vacuum defueling system.